Safety joint



y 7, 1968 R. DUDMAN 3,381,979

SAFETY JOINT Filed Feb. 14. 1966 fiy/ 12m United States Patent 3,381,979 SAFETY JOINT Roy L. Dudman, Sugar Land, Tex., assignor, by inesne assignments, to Schlumberger Technology Corporation, Houston, Tex., a corporation of Texas Filed Feb. 14, 1966, Ser. No. 527,193 6 Claims. (Cl. 285--81) ABSTRACT OF THE DISCLOSURE The particular embodiment described herein as illustrative of one form of the invention in safety joints used in well bores includes telescopically related inner and outer members having coengageable means for limiting telescoping movement. Selectively engageable means are provided between the members operable by longitudinal and rotational motion of one of the members relative to the other for rendering the coengageable means inactive so that the members can be withdrawn from telescoping relation to each other. In order to prevent premature inactivation of the coengageable means, a low pressure seal chamber is provided between the members which are formed in such a manner that fluid pressure in the well bore will exert force on the members in directions tending to maintain the telescoping relationship of the members.

The present invention relates to a safety joint, and, more particularly, to a safety joint having a pressure bias system to prevent its inadvertent operation.

In the operation of well tools in a well bore, the tools sometimes become stuck and prevent their removal from the well bore. It has, therefore, been the practice to include a safety joint in such strings of tools for providing a release mechanism to separate the string above the stuck portion thereby permitting removal of the tool string thereabove. Various arrangements are used in the construction of safety joints. However, the accidental or inadvertent operation of safety joints has heretofore been a problem. If the safety joint is inadvertently operated, a fishing operation is then required to retrieve the released portion of the tool string from the well bore. This is naturally a costly and time-consuming operation.

It is, therefore, an object of the present invention to provide a new and improved safety joint which includes a pressure bias system for preventing inadvertent or accidental operation of the safety joint.

Summary of the invention This and other objects may be attained in accordance with the concepts of the present invention by an apparatus comprising telescopically related inner and outer members having coengageable means for limiting telescoping movement of said members. Selectively engageable means are provided between said members which are operable by manipulation of said members relative to one another to render said coengageable means inactive and permit withdrawal of said members from telescoping relation to each other. The combination further comprises hydraulic means responsive to fluid pressure in a well bore for exerting force on said members in directions tending to maintain the telescoping relation of said members, so that said force must be overcome in order to operate said selectively engageable means and render said coengageable means inactive. It will thus be apparent that the present invention provides a new and improved safety joint which includes a pressure bias system for preventing accidental or inadvertent operation of the joint in a Well bore.

The novel features of the present invention are set forth with particularity in the appended claims. The present invention, both as to its organization and manner of ice operation together with further objects and advantages thereof, may best be understood by way of illustration and example of an embodiment when taken in conjunction with the accompanying drawings in which:

FIG. 1 shows a safety joint embodying the principles of the present invention;

FIG. 1A is a crosss ectional view of the safety joint taken along lines 1A1A of FIG. 1; and

FIG. 2 is a developed view of abutment members forming a part of the safety joint releasing mechanism.

Referring now to FIGURE 1, a safety joint is shown having a tubular mandrel 13 telescopically received within a tubular housing 14, the mandrel and housing having threaded end portions to facilitate their coupling int-o a string of tools. A threaded nut 15 is positioned between the mandrel 13 and housing 14 and engages threads 20 formed on the upper end of the housing is. The nut has an internal spline groove 23 formed thereon which cooperates with an external spline 24 on the mandrel 13. This spline arrangement provides for longitudinal movement between the mandrel and housing of the safety joint and also permits the rotational movement of the mandrel 13 to be transmitted to the nut 15 to rotate the nut relative to the housing. A flange 45 formed on the mandrel 13, limits the upward longitudinal travel of the mandrel with respect to the housing.

Two sets of lugs 46A, 46C and 46B, 46D are formed on the mandrel below the flange 45. The lugs in each set are spaced on the mandrel 180 from each other and the sets are longitudinally spaced on the mandrel. Therefore, each of the lugs is spaced from the adjacent lug and is positioned longitudinally ihereof. A longitudinal key 47 is positioned in the wall of the housing 14 and extends into the annular space between the housing and the mandrel. The key has a longitudinal dimension which is greater than the longitudinal distance between the sets of lugs 46B, 46D and 46A, 460. An annular shoulder portion or sleeve piston 48 is constituted as a lower portion of the housing 14 and has annular recesses formed therein for receiving seal members 49. The shoulder portion 48 is arranged to slidably and sealingly engage the lower end of the mandrel 13 and thereby seal the mandrel bore 51 from communication with a chamber 52 formed between the mandrel and housing.

The upper end of the chamber 52 is enclosed by an outwardly extending annular shoulder portion or sleeve piston 53 which is constituted as a lower portion of the mandrel 13. Annular recesses are formed on the shoulder 53 for receiving se'al members 55. It is readily seen that when the safety joint is assembled, air at atmospheric pressure will be trapped in the chamber 52 and maintained therein by the sealed shoulder portions 48, 53. The shoulder portion 48 on the housing provides an enlarged crosssectional area of the housing below the chamber 52. This enlarged area is denoted by arows aa. The smaller cross-sectional area of the housing above the chamber 52 is denoted by arrows b-b. This arrangement of differential cross-sectional areas of the housing on either side of chamber 52 provides for an imbalance of forces acting against the housing 14 above and below the chamber 52 so that fluid pressure in the well bore will tend to force the housing 14 upwardly relative to the mandrel 13. Likewise an imbalance of forces acts on the mandrel so that fluid pressure will tend to force the mandrel down relative to the housing. These forces acting on the mandrel and housing tend to move the mandrel and housing to a contracted telescoping position.

FIG. 2 shows, in a developed view, the relationship between the lugs 46A46D and the key 47 as the safety joint is operated. In the starting position shown in the top diagram, the lugs and key are positioned as shown in the elevational view of FIG. 1, and cross-sectional view of FIG. 1A, that is, with the lug 46A positioned abutting the key 47. The-second diagram shows that if the mandrel 13 is raised relative to the housing 14 and rotated clockwise, the lug A will be positioned above the key and Will rotate with the mandrel until the lug B abuts the key 47. The third diagram shows that subsequently if the mandrel 13 is lowered relative to the housing the lug B will drop below the key 47 and upon rotation of the mandrel clockwise, will rotate relative to key 47 until the lug C abuts the key 47. Thereafter, another upward movement on the mandrel and clockwise rotation of the mandrel will raise the lug C above the key and rotate it relative to the key until the lug D abuts the key 47, thus completing 270 of rotative movement of the mandrel in the four diagrams shown in FIG. 2. As the mandrel 13 is rotating relative to the housing 14, the spline groove 23 and spline 24 located on the nut and mandrel, respectively, are meshed to rotate the nut 15 with the mandrel 13. If the longitudinal rotative movement described relative to FIG. 2 is repeated enough times the nut 15 will be unscrewed from the mandrel 14 whereupon the mandrel 13 will be free to be withdrawn from the housing 14 thereby releasing or freeing tool members positioned in the tool string above the safety joint for withdrawal from the well bore.

Other Well tools in the tool string are also commonly operated by rotative and longitudinal movement of the well tool members. Therefore, it is possible for inadvertent operation of the safety joint to occur if the sequence of operations of the other well tools were to coincide with the manipulative operation required to operate the safety joint.

In accordance with the present invention means are provided for preventing such inadvertent operation. It is readily seen that when the safety joint is positioned in a well bore, the hydrostatic pressure of well fluids therein will act on the surfaces of the apparatus. By examining the forces acting on the housing 14, it is seen that, under pressure, the housing would tend to move upwardly against the atmospheric pressure trapped in chamber 52. Therefore, if the safety joint mandrel is raised, the housing will tend to raise with it and permit very little if any relative movement between the mandrel 13 and housing 14.

On the other hand, if the housing 14 is attached to a member which is stuck in the well bore, an upward force on the mandrel which is less than the force holding the stuck portion and greater than the bias force on the mandrel and housing holding the members contracted, will move the mandrel upwardly relative to the housing.

Such relative movement will then permit the relative longitudinal movement of the housing and mandrel necessary to operate the safety joint for disengagement of the nut 15 and separation of the parts of the safety joint.

While a particular embodiment of the present invention 4 has been shown and described, it is apparent that changes and modifications may be made without departing from this invention in its broader aspects and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

What is claimed is:

1. In a safety joint for use in a string of tools in a well bore, the combination comprising: telescopically related inner and outer members; coengageable means on said members for limiting telescoping movement of said members; selectively engageable means between said members operable by manipulation of one of said members relative to the other for rendering said coengageable means inactive, whereby said members can be withdrawn from telescoping relation to each other; and hydraulic means responsive to fluid pressure in a well bore for exerting force on said members in directions tending to maintain the telescoping relation of said members, so that said force must be overcome in order to operate said selectively engageable means and render said coengageable means inactive.

2. The apparatus of claim 1 wherein said hydraulic means includes a sealed chamber formed said first and second members, said chamber being at a pressure which is less than the hydrostatic pressure of well fluids in a well bore.

3. The apparatus of claim 1 wherein said hydraulic means includes respective sleeve pistonson each of said tubular members and slidably engaging each other, and seal means on said sleeve pistons forming a sealed low pressure chamber.

4. The apparatus of claim 1 wherein said hydraulic means includes a sealed chamber formed between portions on said tubular members, with one of said members having a differential cross-sectional area above and below said chamber.

5. The apparatus of claim 1 wherein said coengageable means includes a threaded abutment between said tubular members, and abutment means on one of said tubular members engageable with said threaded abutment.

6. The apparatus of claim 5 further including means for corotatably and slidably coupling said one tubular member to said threaded abutment.

References Cited UNITED STATES PATENTS 2,853,265 9/1958 Clark 28S-307 X 3,291,152 12/1966 Comer 28583 X EDWARD C. ALLEN, Primary Examiner.

CARL W. TOMLIN, Examiner.

W. L. SHEDD, Assistant Examiner. 

